Yeon-Su Park

Size-Selective Growth and Stabilization of Small CdSe Nanoparticles in Aqueous Solution

Using cysteine and its derivatives as capping molecules, we investigated the influence of the physical structure and chemical nature of capping molecules on the selective growth and stabilization of small CdSe nanoparticles (NPs) in aqueous solution at room temperature. Our investigations revealed specific roles for each functional group of cysteine, and we could correlate this structure and nature of the capping molecules with the size, size restriction, size distribution, and stability of the NPs. For selective growth and stabilization of the NPs in aqueous solution, their capping molecules should have at least one functional group with strong nucleophilicity as well as another free, charged functional group. Capping molecules acting as a monodentate ligand were more effective than those acting as a bidentate ligand for restricting the NPs to a smaller size, whereas the former was less effective than the latter for getting a narrower NP size distribution. Capping molecules with relatively bulky spatial geometry near the ligand-NP interface resulted in the formation of NPs with poor short- and long-term stabilities, whereas those having relatively compact spatial geometry near the interface led to NPs with at least moderate short-term stability. We saw that capping molecules having relatively compact outermost spatial geometry led to NPs with excellent long-term stability, whereas those having relatively bulky outermost spatial geometry produced NPs with at most only moderate long-term stability. Our results clearly showed general trends for the possibility of selective growth of stable semiconductor NPs with particular sizes in aqueous solution.

Lipid nanocapsules for intracellular drug delivery of anticancer drugs.

Very stable and small CdSe nanoparticles (NPs) were synthesized from the aqueous solutions containing L-cysteine (Cys) at room temperature. The Cys-capped CdSe NPs showed a very sharp excitonic peak at 420 nm. Its very small full width at half maximum (18 nm) indicates very high quality of the CdSe NPs. Their absorption features experienced little change over a month, implying an excellent stability of the CdSe NPs. The synthesis conditions were very critical to the optical property and stability of the CdSe NPs: only those prepared at specific conditions (n(Se-precursor)/n(Cd-precursor) = 0.25-0.5, n(Cys)/n(Cd-precursor) = approximately 9, pH = approximately 12) showed very sharp absorption peaks and maintained an excellent stability against time. Under these conditions, the peaks always appear at nearly the same wavelength, indicating that these NPs are selectively stable and grow at a particular size and structure.

Cell separation by the combination of microfluidics and optical trapping force on a microchip

AbstractWe investigated properties of cells affecting their optical trapping force and successfully established a novel cell separation method based on the combined use of optical trapping force and microfluidics on a microchip. Our investigations reveal that the morphology, size, light absorption, and refractive index of cells are important factors affecting their optical trapping force. A sheath flow of sample solutions created in a microchip made sample cells flow in a narrow linear stream and an optical trap created by a highly focused laser beam captured only target cells and altered their trajectory, resulting in high-efficiency cell separation. An optimum balance between optical trapping force and sample flow rate was essential to achieve high cell separation efficiency. Our investigations clearly indicate that the on-chip optical trapping method allows high-efficiency cell separation without cumbersome and time-consuming cell pretreatments. In addition, our on-chip optical trapping method requires small amounts of sample and may permit high-throughput cell separation and integration of other functions on microchips. FigureOptical trapping in a microchannel allows high-efficiency separation of cells, e.g., dead and live HeLa cells

On-chip fabrication of mutifunctional envelope-type nanodevices for gene delivery

Microfluidic devices may be highly beneficial to the rapid fabrication of small quantities of various nonviral vectors with different functionalities, which is indispensable for effective order-made gene therapy. We adapted a microfluidic chip-based approach for fabricating small quantities of nonviral vectors in a short time in preparation for order-made gene therapy applications. This approach permitted us to fabricate multifunctional envelope-type nanodevices (MENDs), composed of a compacted (or condensed) DNA core and a lipid bilayer membrane shell, which are considered as promising nonviral vectors for gene therapy applications. The on-chip fabrication of the MEND was very simple, rapid, convenient, and cost-effective compared with conventional methods. The size of the MEND showed strong dependence on the concentration and flow rate of the reaction precursors and could be controlled to be much smaller than that achievable by conventional methods. This, together with abovementioned merits, makes our microfluidic chip-based approach very attractive for the fabrication of MENDs for effective application to order-made gene therapy.

Fabrication of functionalized double-lamellar multifunctional envelope-type nanodevices using a microfluidic chip with a chaotic mixer array.

Multifunctional envelope-type nanodevices (MENDs) are very promising non-viral gene delivery vectors because they are biocompatible and enable programmed packaging of various functional elements into an individual nanostructured liposome. Conventionally MENDs have been fabricated by complicated, labor-intensive, time-consuming bulk batch methods. To avoid these problems in MEND fabrication, we adopted a microfluidic chip with a chaotic mixer array on the floor of its reaction channel. The array was composed of 69 cycles of the staggered chaotic mixer with bas-relief structures. Although the reaction channel had very large Péclet numbers (>105) favorable for laminar flows, its chaotic mixer array led to very small mixing lengths (<1.5 cm) and that allowed homogeneous mixing of MEND precursors in a short time. Using the microfluidic chip, we fabricated a double-lamellar MEND (D-MEND) composed of a condensed plasmid DNA core and a lipid bilayer membrane envelope as well as the D-MEND modified with trans-membrane peptide octaarginine. Our lab-on-a-chip approach was much simpler, faster, and more convenient for fabricating the MENDs, as compared with the conventional bulk batch approaches. Further, the physical properties of the on-chip-fabricated MENDs were comparable to or better than those of the bulk batch-fabricated MENDs. Our fabrication strategy using microfluidic chips with short mixing length reaction channels may provide practical ways for constructing more elegant liposome-based non-viral vectors that can effectively penetrate all membranes in cells and lead to high gene transfection efficiency.

Preparation of concentrated colloids of gold core-silica shell nanoparticles for biomedical applications.

Encapsulation of gold nanoparticles within a silica shell is highly beneficial to the preparation of highly concentrated gold nanoparticles that can strongly absorb X-ray and hence be used as an X-ray contrast agent. This chapter describes a method for preparing highly concentrated colloidal gold nanoparticles suitable for an X-ray contrast agent application. It describes specific details of procedures for preparing spherical gold nanoparticles, forming thin silica shell on each gold nanoparticle, and enriching the silica-encapsulated gold nanoparticles.

Size-Selective Synthesis of Ultrasmall Hydrophilic CdSe Nanoparticles in Aqueous Solution at Room Temperature

Hydrophilic semiconductor nanoparticles are very attractive for various biological applications, such as in optical sensing, tracing, and imaging of biological molecules-of-interest, because of their broad excitation wavelength, tunable emission wavelength, strong photoluminescence, and relatively high stability against photobleaching and chemicals. Compared to organic phase synthesis and subsequent surface modification, aqueous phase synthesis approaches provide multiple advantages for obtaining hydrophilic semiconductor nanoparticles. Here, we describe methods for the size-selective growth and stabilization of ultrasmall hydrophilic CdSe nanoparticles in aqueous solution at room temperature by using amino acid cysteine or one of its derivatives as a surface capping agent.